Lead casing for pencil, and pencil thereof for writing, drawing, marking, plotting, and coloring

ABSTRACT

There is a lead casing for pencil for writing, drawing, marking, plotting, and/or coloring made of a composition having, by weight relative to the total weight of the lead casing for pencil: a) from 50 to 95% of a mixture of polylactic acid and polybutylene adipate terephtalate in a weight ratio polylactic acid/polybutylene adipate terephtalate ranging from 60/40 to 90/10, and b) from 5 to 40% of mineral fillers chosen in the group consisting of shellfish shells, more specifically oyster shells, and even more specifically milled oyster shells.There is also a pencil including the lead casing for the pencil of the disclosure, for writing, drawing, marking, plotting, and/or coloring as well as a method for manufacturing such a pencil.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage Application of InternationalApplication N°PCT/EP2019/085561, filed on Dec. 17, 2019, now publishedas WO2020/127203, which claims priority to EP18306713.1, filed on Dec.18, 2018, the entire contents of both of which are incorporated hereinby reference.

FIELD OF THE DISCLOSURE

The present disclosure relates to a polymer-based lead casing forpencil. The disclosure also relates to a method for manufacturing apencil comprising a lead casing according to the disclosure. Finally,the disclosure relates to the use of a pencil comprising a lead casingfor pencil according to the disclosure for writing, drawing, marking,plotting, and/or coloring.

DESCRIPTION OF THE RELATED ART

Two main families of thermoplastic polymers are used today in syntheticlead casings for pencils: styrenics such as polystyrene (PS) andacrylonitrile butadiene styrene (ABS) and polyolefins such aspolyethylene (PE) and polypropylene (PP). These polymers are all fromthe petroleum industry. For ecological reasons, it would be interestingto be able to replace such thermoplastic polymers with biorenewablepolymers.

The patent application FR2988643 describes a pencil whose lead casing(called the envelope portion in the application) is based on expandedsynthetic material. It teaches that the thermoplastic materials of thelead casing portion and the lead portion may be selected from styrenicpolymers such as polystyrene, polyolefins and biopolymers. Polylacticacid (PLA) is thus the only biopolymer cited, although the only exampleof lead casing is based on a polymer matrix of the styrenic family.

SUMMARY OF THE DISCLOSURE

The inventors have now observed that the use of PLA as the solethermoplastic polymer in the lead casing for pencil did not make goodmechanical properties in terms of resilience and impact resistance,which can cause problems in the manufacturing process and the sharpnessof the final pencil. Thus, PLA “alone” does not make a good substitutefor polymers derived from petroleum such as polystyrene in themanufacture of the lead casing for pencil.

The inventors, however, surprisingly observed that it was possible tomanufacture a lead casing for pencil having better mechanical propertiesto polystyrene-based lead casings by using as a thermoplastic polymer amixture of PLA with polybutylene adipate terephtalate (PBAT), anotherbiopolymer, in specific proportions, in combination with an appropriatecontent of mineral fillers chosen in the group consisting of shellfishshells, more specifically milled shellfish shells, even morespecifically oyster shells, and even more specifically milled (orcrushed) oyster shells.

The present disclosure therefore relates to a lead casing for pencilwhich is made of a composition comprising (more specifically consistingessentially of, in particular consisting of), by weight relative to thetotal weight of the lead casing for pencil:

-   a) from 50 to 95%, more specifically from 60 to 95%, and even more    specifically from 70 to 90%, of a mixture of PLA and PBAT in a    weight ratio PLA/PBAT ranging from 60/40 to 90/10, and-   b) from 5 to 40%, more specifically from 7 to 30%, of mineral    fillers chosen in the group consisting of shellfish shells, more    specifically milled shellfish shells, even more specifically oyster    shells, and even more specifically milled (or crushed) oyster    shells.

Such polymer-based lead casings for pencil are intended to replacetraditional lead casings made of wood, and may be referred to “syntheticwood” or “body/core synthetic”. They allow the gripping of pencil andprotect the lead against breakage. They must be resistant to deformationfor not being bended or twisted, which would break the lead from inside.They must also be able to be cut by a traditional sharpener. They aregenerally made of polymer-based synthetic material whose density andsharpness are similar to those of wood and can be extruded. They can beexpanded.

They also have no splinters if the pencil breaks because they are basedon polymeric material.

DETAILED DESCRIPTION OF THE DISCLOSURE

According to a preferred embodiment, the lead casing for pencil of thedisclosure is made of a composition comprising (more specificallyconsisting essentially of, in particular consisting of), by weightrelative to the total weight of the lead casing for pencil:

-   a) from 70 to 90% of a mixture of PLA and PBAT in a weight ratio    PLA/PBAT ranging from 60/40 to 90/10, and-   b) from 7 to 30% of mineral fillers chosen in the group consisting    of shellfish shells, more specifically milled shellfish shells, even    more specifically oyster shells, and even more specifically milled    (or crushed) oyster shells.

According to a preferred embodiment, the lead casing for pencil of thedisclosure is made of a composition comprising (more specificallyconsisting essentially of, in particular consisting of), by weightrelative to the total weight of the lead casing for pencil:

-   a) from 80 to 90% of a mixture of PLA and PBAT in a weight ratio    PLA/PBAT ranging from 65/35 to 85/15, and-   b) from 10 to 20% of mineral fillers chosen in the group consisting    of shellfish shells, more specifically milled shellfish shells, more    specifically oyster shells, and even more specifically milled (or    crushed) oyster shells.

The lead casing for pencil of the disclosure thus comprises a mixture ofPLA, for example commercially available from NaturePlast, and PBAT, forexample commercially available from NaturePlast, in a weight ratio ofPLA/PBAT ranging from 60/40 to 90/10, in particular from 65/45 to 80/20,more particularly from 70/30 to 80/20, and even more particularly in aweight ratio of 70/30.

This mixture of biodegradable thermoplastic polymers serves as a matrixfor the lead casing for pencil of the disclosure and makes it possibleto manufacture the lead casing by extrusion and to provide goodmechanical properties such as resilience and impact resistance. It alsomakes it possible to bring the trimming to the lead casing for pencil ofthe disclosure. The content of the mixture of PLA and PBAT in the leadcasing for pencil of the disclosure thus ranges from 50 to 95%, morespecifically from 60 to 95%, even more specifically from 60 to 92%, evenmore specifically from 70 to 90%, and even more specifically from 80 to90%, by weight relative to the total weight of the lead casing forpencil.

The lead casing for pencil of the disclosure further comprises mineralfillers chosen in the group consisting of shellfish shells. Theshellfish shells are more specifically oyster shells or scallop shells,even more specifically oyster shells, and even more specifically milled(or crushed) oyster shells. In particular, the mineral fillers arechosen in the group consisting of milled oyster shells, morespecifically in the form of crushed shells, in particular commerciallyavailable from NaturePlast. The mineral fillers make it possible toimprove the mechanical properties of the lead casing for pencil such asthe flexural modulus (3 points).

More specifically shellfish shells, even more specifically milledshellfish shell, and even more specifically milled (or crushed) oystershells, have a volume-average diameter (d50) ranging more specificallyfrom 10 to 160 μm, in particular from 20 to 100 μm, and even morespecifically from 30 to 80 μm, and still more specifically of 70 μm. Thevolume-average diameter (d50) can for example be measured by laserparticle sizing with a Mastersizer 3000 type apparatus commerciallyavailable from Malvern.

More specifically, the mineral fillers of the disclosure are combinedwith additional fillers, more specifically different from shellfishshells, and even more specifically different from milled (or crushed)oyster shells. More specifically, the additional fillers can bevegetable fillers, more specifically wood fibers, even more specificallyin the form of powder, in particular commercially available from JRSRettenmaier or CFF GmbH & Co. KG or Jelu-Werk or Rossow. The fillers cantherefore consist of a mixture of oyster shells and wood fibers, inparticular a mixture of milled (or crushed) oyster shells and woodfibers.

The total content of fillers (mineral fillers+additional fillers) in thelead casing for pencil of the disclosure may range from 5 to 50%, morespecifically from 7 to 40%, even more specifically from 8 to 30%, morespecifically still from 9 and 20%, and in particular 10% by weight, withrespect to the total weight of the lead casing for pencil.

The content of mineral fillers in the lead casing for pencil of thedisclosure ranges from 5 to 40%, more specifically from 7 to 30%, evenmore specifically from 10 to 20%, and in particular 15%, by weightrelative to the total weight of the lead casing for pencil.

The lead casing for pencil of the disclosure may further comprise anadhesion promoter. If the adhesion promoter is present, its contentranges from 0.1 to 10%, more specifically from 1 to 5%, even morespecifically from 2 to 5%, and even more specifically from 1 to 3%, byweight relative to the total weight of the lead casing for pencil. Theadhesion promoter makes it possible to improve the adhesion between thethermoplastic polymer (mixture of PLA and PBAT) and the mineral fillers.

Thus, in a particular embodiment, the lead casing for pencil of thedisclosure comprises mineral fillers which consist of shellfish shells,in particular milled shellfish shells, more specifically oyster shells,and more specifically milled (or crushed) oyster shells, alone orpossibly mixed with vegetable fillers, more specifically wood fibers,even more specifically in the form of powder, the lead casing for pencilalso comprising an adhesion promoter as defined according to thedisclosure.

In a preferred embodiment, the adhesion promoter of the disclosure is apolylactic acid grafted with maleic anhydride (PLA-MA), for examplecommercialized by NaturePlast or NatureWorks.

The lead casing for pencil of the disclosure may comprise otheradditives, such as, for example, dyes and/or pigments, in particular inthe form of a masterbatch, for example based on PLA, blowing agents,agents for use, lubricants, slip agents such as stearates (calciumstearate for example) and/or stearamide, performance modifiers of PLA(melt enhancer which improve the strength/consistency of the extrusionmelt), in particular acrylics, and a mixture of these additives.

The content of additive in the lead casing for pencil of the disclosurewhen present ranges from 0.1 to 10%, and more specifically from 3 to 8%by weight, by weight relative to the total weight of the lead casing forpencil.

In particular, the lead casing for pencil of the disclosure may comprisea blowing agent, for example consisting of expandable and imperviousparticles, the wall of which is made of an extensible polymer material.Under the effect of temperature, a chemical or physical reaction occurswithin the particles, causing an increase in the internal volume of theparticles and their expansion. Thus, the blowing agent may be chosenfrom microspheres having a shell and enclosing a gas or a gas mixture.An increase in temperature causes an increase in the internal pressureof the microspheres that swell to a size that can be multiplied by fiveor more. Depending on the desired result of flexibility, weight, and anyother property of the material in which the blowing agent isincorporated, the expansion is completed or not.

Moe specifically, the blowing agent is introduced into the compositionof the lead casing in a content ranging from 0.1 and 1%, and even morespecifically from 0.5 and 1%, by weight relative to the total weight ofthe lead casing for pencil. The blowing agent is more specificallychosen in the group consisting of citric acid, sodium bicarbonate, ormixture thereof.

The lead casing for pencil of the disclosure may also comprise dyesand/or pigments (such as red iron oxide), in particular in the form of amasterbatch, more particularly based on PLA. The content of dyes and/orpigments more specifically ranges from 0.1 to 10% by weight, inparticular if the dye and/or the pigment is not in the form of amasterbatch, even more specifically from 0.1 to 5% by weight, and evenmore specifically from 0.5 and 3% by weight, relative to the totalweight of the lead casing for pencil of the disclosure. In a preferredembodiment, the dyes and/or pigments are capable of providing a colorclose to the wood to the lead casing for pencil of the disclosure.

The lead casing for pencil of the disclosure may be made of acomposition wherein the sum of weight % of component a) (mixture of PLAand PBAT), components b) (mineral fillers) and optional othercomponent(s) such as additional fillers, adhesion promoters, dyes,pigments, blowing agents, agents for use, lubricants, slip agents,performance modifiers, etc., represents 100%.

The lead casing for pencil of the disclosure is more specificallyextrudable. It is also more specifically shaped and can have inparticular the density and the sharpness approximating those of wood. Inparticular, the pencil can be cut by a traditional pencil sharpener.Therefore, it is not the lead casing for pencil of a mechanical pencil.

The present disclosure further relates to a pencil for writing, drawing,marking, plotting, and/or coloring, comprising a lead casing for pencilaccording to the disclosure. The pencil of the disclosure is not amechanical pencil.

In the pencil of the disclosure, the lead casing more specificallysurrounds, in particular concentrically, the lead or a protectiveintermediate layer disposed between the lead and the lead casing of thedisclosure. In a particular embodiment of the disclosure, the pencil ofthe disclosure comprises an additional layer of decoration, morespecifically varnish, surrounding, in particular concentrically, thelead casing of the disclosure. More specifically, the decorative layeris made of a material compatible with that of the lead casing of thedisclosure.

According to a preferred embodiment, the lead of the lead casing of thedisclosure is a polymer-based lead, and not a calcined lead.

In a particular embodiment of the disclosure, the pencil of thedisclosure is obtained by extrusion, in particular by coextrusion of thelead/optional protective layer/lead casing according to thedisclosure/optional decorative layer. In a preferred embodiment, thecoextrusion makes it possible to prepare in a single step a continuousring consisting of the four aforementioned layers of the pencil, thesebeing assembled in the chosen order lead/optional protective layer/leadcasing according to the disclosure/optional decorative layer. For this,four single-screw extruders each delivering the material constituting alayer are connected in a coextrusion head tooling associating in theright order the layers between them. Multiple extrusion techniques arewell known to the person skilled in the art. By way of example, suchmethods for continuously manufacturing pencils are described in documentU.S. Pat. No. 6,572,295.

According to a preferred embodiment, the pencil of the disclosure is agraphite pencil and/or a colored pencil. The formulation of the lead mayvary depending on whether the pencil is a graphite pencil or a coloredpencil. An example of formulation of a graphite lead is described in theapplication WO2016/097553. The formulation of a colored lead may existin two forms: polyolefin-based erasable formulation as described in theapplication WO2016/097555 or styrenic-based standard formulation asdescribed in the application WO2017/220914.

In a particular embodiment of the disclosure, the lead has a diameter ofbetween 2 and 3.6 mm. In a graphite pencil, the diameter of the lead maymore specifically vary from 2 to 2.5 mm. In a colored pencil, thediameter of the lead may more specifically vary from 3 to 3.5 mm.

In the case of a graphite pencil, carbon black may be added to the lead,and thus considered as a pigment. In this case, graphite may vary from40 to 60% by weight and carbon black from 0 to 10% by weight, relativeto the total weight of the lead.

The pencil of the disclosure more specifically has a hexagonal, round ortriangular section, even more specifically round or hexagonal.

More specifically, the pencil of the disclosure comprises means forerasing, such as an eraser, at the uncut end of the pencil.

In addition to the above provisions, the disclosure also comprises otherprovisions which will emerge from the remainder of the description whichfollows.

EXAMPLES

Two compositions A and B of lead casing were prepared.

Composition A (invention) was a mixture of PLA/PBAT (NaturePlast PLE005-1 and PBE 006) in a weight ratio of 80/20, added with 15% by weightof milled oyster shells (from NaturePlast).

Composition B (comparative) was a mixture of polylacticacid/polybutylene succinate PLA/PBS (NaturePlast PLE 005-1 and PBE 003)in a weight ratio of 70/30, added with 10% by weight of milled oystershells (from NaturePlast).

Pencils with hexagonal section were manufactured by coextrusion with acolor lead made of acrylonitrile-butadiene-styrene (ABS) (composition in% by weight relative to the total weight of the lead: 40% ABS copolymer,12.5% kaolin, 27.5% calcium stearate, 20% additive), a sheath, a leadcasing of composition A (invention) or of composition B (comparative),and a varnish. The thickness of the lead casing is 4.5 mm.

The performances of the pencils made of the lead casings of compositionsA and B were tested according to the following tests:

The pencil flexural resistance test was carried out in order to checkthe strength and the crack resistance of the pencil.

The characteristics of the test were as follows:

Equipment: Dynamometer LLOYD-AMETEK Instrument type, U-bracket span of 6cm, Sensor ADAMEL DY20 Chatillon Instrument type TCD110 50 daN

Descent speed of sensor: 50 mm·min⁻¹

Operating Method:

1. Turn on the dynamometer.

2. Locate the sensor in the up position.

3. Fix the pencil on the U-bracket.

4. Go down the needle.

5. Record the results expressed in daN.

The lead resistance at 45° was carried out with a Dynamometer Chatilloninstrument type TCM 201-M.

Operating Mode:

1. Position the pencil in a support with a 45° inclination, descend thepencil at a descent speed of 50 mm·min⁻¹, and come into contact with ametal plate until the lead breaks.

2. Read the value of the result displayed on the dynamometer.

The result was the measure of the force required to break the mine,expressed in daN.

The performances of the pencils made of the lead casings of compositionsA and B are summarized in the following Table 1:

TABLE 1 Composition A Composition B (invention) (comparative) Pencilflexural resistance (daN) 8.60 8.37 Lead resistance at 45° (daN) 1.831.20

The results presented in Table 1 show better flexural resistance andlead resistance at 45° , for the pencil according to the disclosure madeof the lead casing of composition A with respect to the comparativepencil made of the lead casing of composition B. A higher pencilflexural resistance means that the pencil of the disclosure resistsbetter to flexing forces and is therefore more resistant to break duringflexing.

1-12. (canceled)
 13. A lead casing for a pencil, comprising acomposition including, by weight relative to the total weight of thelead casing for the pencil: a) from 50 to 95% of a mixture of polylacticacid and polybutylene adipate terephtalate in a weight ratio polylacticacid/polybutylene adipate terephtalate ranging from 60/40 to 90/10, andb) from 5 to 40% of mineral fillers selected from the group consistingof shellfish shells.
 14. A lead casing for the pencil according to claim13, comprising, by weight relative to the total weight of the leadcasing for the pencil: a) from 60 to 95%, of a mixture of polylacticacid and polybutylene adipate terephtalate in a weight ratio polylacticacid/polybutylene adipate terephtalate ranging from 60/40 to 90/10, andb) from 7 to 30%, of mineral fillers selected from the group consistingof shellfish shells.
 15. The lead casing for the pencil according toclaim 13, comprising, by weight relative to the total weight of the leadcasing for the pencil: a) from 80 to 90% of a mixture of polylactic acidand polybutylene adipate terephtalate in a weight ratio polylacticacid/polybutylene adipate terephtalate ranging from 65/35 to 85/15, andb) from 10 to 20% of mineral fillers selected from the group consistingof shellfish shells.
 16. A lead casing for the pencil according to claim13, wherein the weight ratio polylactic acid/polybutylene adipateterephthalate is ranging from 65/45 to 80/20.
 17. The lead casing forthe pencil according to claim 13, wherein the mineral fillers are oystershells.
 18. The lead casing for the pencil according to claim 13,wherein the oyster shells are milled oyster shells.
 19. The lead casingfor the pencil according to claim 13, wherein it further comprises anadditional filler.
 20. The lead casing for the pencil according to claim19, wherein the additional filler is selected from the group consistingof vegetable fillers.
 21. The lead casing for the pencil according toclaim 19, wherein the additional filler is wood fibers.
 22. The leadcasing for the pencil according to claim 13, wherein the total contentof filler ranges from 5 to 50%, by weight with respect to the totalweight of the lead casing.
 23. The lead casing for the pencil accordingto claim 13, wherein the total content of filler ranges from 8 to 30%,by weight with respect to total weight of the lead casing for thepencil.
 24. The lead casing for the pencil according to claim 13,wherein the content of mineral filler ranges from 5 to 40% by weight,relative to the total weight of the lead casing.
 25. The lead casing forthe pencil according to claim 13, further comprising at least oneadditive selected from the group consisting of dyes, pigments, blowingagent, agents for use, lubricants, slip agents, performance modifiers ofpolylactic acid, and their mixtures.
 26. The lead casing for the pencilaccording to claim 13, wherein the additive represents from 0.1 to 10%by weight relative to the total weight of the lead casing for thepencil.
 27. The lead casing for the pencil according to claim 13,further comprising an adhesion promoter.
 28. The lead casing for thepencil according to claim 27, wherein the adhesion promoter is apolylactic acid grafted with maleic anhydride (PLA-MA).
 29. A pencilcomprising a lead casing for the pencil according to of claim 13surrounding a lead.
 30. The pencil according to claim 29, wherein thelead includes at least graphite and/or pigments.
 31. The pencilaccording to claim 29, being a graphite pencil and/or a colored pencil.32. A method for manufacturing a pencil according to claim 29, whereinthe constituents of the lead casing for the pencil are coextruded aroundthe constituents of the lead.